A battery system includes an electrochemical cell. The electrochemical cell includes a cover having an opening therein. The electrochemical cell also includes an aluminum terminal pad disposed proximate an outer surface of the cover, and having a pad opening aligned with the opening in the cover. The pad opening includes a tapered surface such that the pad opening has a larger cross-sectional width proximate an upper surface of the aluminum terminal pad than proximate a lower surface of the aluminum terminal pad opposite the upper surface and facing the outer surface of the cover. The electrochemical cell also includes a rivet having a body portion extending through the opening in the cover, a head portion disposed in the pad opening of the aluminum terminal pad, and a shoulder extending between the body portion and the head portion. The head portion includes an inverted cone shape corresponding with the tapered surface of the pad opening and having a maximum cross-sectional width greater than a minimum cross-sectional width of the pad opening.